STEERING NON-DRIVING WHEELS OF VEHICLES

Abstract: A wheeled vehicle such as a wheel-chair has motor-driven wheels (1) and freely rotating swivel wheels (11, 11'). The motor-driven wheels (1) have shafts fixedly arranged in the vehicle and they are driven individually for steering the vehicle. In order to reduce those instabilities which can arise in the movement of the vehicle, one (11') of the freely rotating wheels is provided with a direction or steering control, so that it can be given a suitable angle in relation to the vehicle and to the movemenet direction thereof. For some movement states the angular direction control can be deactivated so that the freely rotating swivel wheel (11') can adjust itself freely in the usual way. For achieving the angular direction control of the swivel wheel (11') a chain or belt (21) runs about the swivel shaft (13') thereof and it also passes over a wheel (22). This wheel (22) is driven by an electric steering motor (19) through a not self-braking or not irreversible worm gear unit (23). The system steering control motor (19), reduction gear unit (23), chain or belt (21), is as seen as a unit, reversible, which allows a forced control of the angular position of the swivel wheel (11'), when the motor (19) is actively driven when feeding electric current thereto, and that the swivel wheel (11') can adjust itself freely to an arbitrary angular position when no current is fed to the motor (19).

Description: Steering non-driving wheels of vehicles FIELD OF THE INVENTION The present invention relates to a device for steering freely pivotable wheels of wheeled vehicles. BACKGROUND OF THE INVENTION In motor-driven vehicles of type wheel-chairs often two or more wheels are used which are driven by a motor, and the other wheels, which are usually located at the rearmost or frontmost position of the vehicle, are constructed as swivel wheels. Swivel wheels are here wheels which are not motor-driven and which are pivotable about an axis essentially perpendicular to the surface, here generally called ground, on which the vehicle runs, i.e. also perpendicular to the movement direction of the vehicle and also to the rotational axis of the wheel. The swivel shaft has a centre axis in the shape of a straight line passing at a distance from the geometric rotational axis of the wheel itself. Hereby a suspended wheel in that way will be adjusted freely and by itself in the movement of the vehicle on a ground surface, due to the friction of the wheel to the ground. A wheel chair of this type having motor-driven wheels and swivel wheels is conventionally steered when running by giving the motor-driven wheel at one side of the vehicle a velocity different from that of the motor-driven wheel at the other side. For some movement cases, such as for abrupt turns or bends, in running the vehicle with a velocity which is not too low, and in running the vehicle obliquely uphill or downhill, the behaviour of the freely movable swivel wheels can result in difficulties in the operation and the steering of the vehicle, so that the end of the vehicle carrying these swivel wheels will turn out too much (oversteering) and/or so that the desired movement direction, which is adjusted by means of a joystick or some similar device, must be corrected all the time. In a conventional wheel-chair having two driven wheels at the front and two swivel wheels at the rear the point of inertia of the vehicle is in addition usually displaced more close to the two driving wheels which generally also has a larger diameter than the swivel wheels. A common distribution of the weight can be that the larger driven front wheels will carry two thirds of the weight of the wheel-chair, the rear swivel wheels then carrying only one third. When running the wheel-chair and in the operatio of the wheel-chair this weight distribution must be considered. Prior art In the European patent document EP-B1 0 324 101 for Ortopedi GmbH an electrically driven wheel-chair is disclosed having a stabilizing steering. This prior device has a little larger motor-driven wheels 3 and smaller swivel wheels 5 and a seat, which can be rotated, so that the motor-driven wheels 3 can be placed at the front or at the rear, as to what is required. The swivel wheels 5 are steerable by means of an engageable steering actuator 12. In the embodiment of Fig. 2 there is one steering actuator 13 provided for each swivel wheel and comprising a cogged belt 14 transferring the rotational movement of the steering actuator to the vertical shaft 15 of the respective swivel wheel. In a particular embodiment the steering actuator 1 for a swivel wheel 15 can be connected to the vertical swivel shaft 15 through a clutch 17. When the clutch 17 is disengaged, this swivel wheel can pivot freely about its vertical axis. Such a free turning movement is advantageous for fine operations and at a low velocity of the wheel-chair. For higher velocities thereof the steering actuator 13 can be connected or engaged, possibly in such a way that it is always engaged at and exceedin a predetermined velocity. In the embodiment of Fig. 3 a cross bar 20 is arranged connecting levers on the vertical swivel shafts of the two swive wheels 5, so that the pivoting movements thereof are connected. steering actuator 18 acts on one of the levers and can be disengaged. The positions of the swivel wheels are monitored by position sensors 32 and 33, see Fig. 4, which control the engagement of the steering actuator 18. An engagement can thus only be performed for a correct position of the swivel wheels an the steering actuator in relation to each other. The engagement of the steering driving device can take place as commanded manually or automatically within an allowed pivoting range and/o depending on the velocity of the wheel-chair, see Fig. 4. In the embodiment according to Fig. 5 a forced steering is arranged having a steering actuator 18 acting on only one swivel wheel 5, the other swivel wheel being freely pivotable all the time. In this case also, there is one position sensor 33 for the angular position of the swivel wheel 5 about the vertical swivel shaft thereof and one position sensor 33 for the angular position of the clutch 17. In other respects this embodiment operates in the same way as the steering according to Figures 3 and 4. In the embodiment according to Fig. 6 separate forced actuators 18 and disconnectable mechanical clutches 17 are arranged for each swivel wheel 5. The pivot angle of the swivel wheel is controlled by a processor 37. This prior design exhibits a relatively complicated mechanical construction having an electrically controlled mechanical clutch and two position sensors for each steered swivel wheel and a complicated engagement procedure for the steering which is possible only for some angular positions of a steered swivel wheel. DESCRIPTION OF THE INVENTION It is a purpose of the invention to provide a steering of a swivel wheel which can be activated by a simple mechanical device when required. It is a further purpose of the invention to provide an engageable or connectable steering of the swivel wheel which requires only one angular position sensor and a simple electronic control. These purposes are achieved by the invention, the more detailed characteristics of which appear from the appended claims. Thus a wheeled vehicle is provided, like a wheeled chassis for a wheel-chair or a car for the transport of goods. The vehicle has a number of motor-driven wheels which are rotationally driven by one or more motors. These motor-driven wheels are generally placed on the same geometric axis and can for a wheel-chair having six wheels be those wheels which are mounted at the middle shaft. For wheel-chairs having four wheels these wheels are either the front or the rear wheel pair. The vehicle is steered when moving or running over a ground surface by the method that at least two driven wheels can be driven at different velocities in order to cause a turn of the vehicle. The vehicle has further one or more swivel wheels, such as for a wheel-chair having six wheels the rear and front wheel those which are arranged at the ends of the vehicle, and for a wheel-chair having four wheels either the front or the rear wheel pair. One or more of these freely rotating swivel wheels, which thus are not driven by a motor, and preferably onl one thereof, is given a definite angle, which is adjusted all th time in relation to the vehicle during the movement of the vehicle, however preferably only for some movement conditions or movement states for the vehicle. This freely rotatable wheel is given an angle which is determined in order to stabilize the movement of the vehicle and to support and facilitate the transport of the vehicle for instance in curves or bends or on slopes, in particular when running obliquely on sloping planes. The preferred mechanical construction of the steering or direction control comprises that the swivel wheel which is steered, is provided with a swivel pin or swivel shaft which can be prolonged for this purpose. Around the swivel pin there passe an endless element, such as a chain, a cogged belt, and this element also passes over a suitable wheel driven by a steering motor through a transmission unit such as a worm gear unit. This stiff mechanical transmission between the swivel pin of the freely rotating wheel and the motor of the steering control is further not self-braking or irreversible, i.e. it is reversible, and the motor possesses a little inherent inertia, so that for a deactivation of the motor, i.e. when it is an electric motor and the windings thereof are not provided with electric current, the swivel pin, which is otherwise controlled by force, can freely move or pivot in dependence only of those forces which originate from the freely rotating wheel itself and which are produced at the contact of the wheel with the ground in the movement of the vehicle. In order to generate feedback signals to be provided to the control motor, which indicates the rotational or pivoting movement of the swivel wheel, and possibly to a superior control circuit, an angular sensor is provided at the swivel pin, generating signals which indicate the angular position of the swivel pin in relation to the vehicle itself or to a frame or chassis thereof. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described as a not limiting embodiment of the invention with reference to the accompanying drawings in which Fig. 1 shows, schematically as seen from the side, a wheeled chassis for a motor-driven wheel-chair, Fig. 2 shows the chassis as seen from above, Fig. 3 shows the chassis as seen from the rear, Fig. 4 shows a block diagram of electric control circuits fo the wheeled chassis and Fig. 5 shows a steering drive motor with an associated worm gear unit. PREFERRED EMBODIMENT In the Figures 1 - 3 a wheeled chassis for a wheel-chair is illustrated, where the seat itself is not drawn. The chassis has two driven larger front wheels 1. In a normal movement of the wheel-chair the wheels 1 thereof are located in the frontmost position as seen in the movement direction, as is also indicated by an arrow in Fig. 1. The front wheels 1 are each one driven individually by a separate motor 3. The operation of the motors 3 is controlled by means of control circuits 5 which in turn obtai commands from some manual steering device, such as a joystick or other steering lever, not illustrated. The motors 3 and the control circuits 5 are carried by a frame 7. Further, on the frame 7 battery cases are arranged with electric accumulator batteries 9 comprised therein, from which the motors 3 obtain th energy necessary for their operation through lines, not illustrated in the Figures. The rear wheels 11 and 11' of the chassis are of the type swivel wheels and their swivel pins or swivel shafts 13 and 13' respectively are supported by rear frames 15 and 15' respectively. Each rear frame 15 or 15' is further hinged to the main chassis 7. The two rear frames are semi-stiffly connected with each other by means of an elastic buffer 18 so that they will always be in essentially the same position in relation to each other but can elastically move away from this position when running on a rough ground. The rotational axis of the hinge 17 i located in essentially the longitudinal direction of the chassis, i.e. substantially in parallel to the movement direction when running the wheeled chassis straight ahead or straight backwards. The rear frames 15 and 15' can hereby swing upwards or downwards in relation to the main frame 7 when the swivel wheels 11 and 11' run on a rough ground surface, where they will occupy different levels . One of the swivel wheels 11, 11', in the embodiment illustrated in the drawings the right rear wheel 11', has its swivel pin 13' prolonged upwards so that the swivel pin protrudes above the rear frame 15 to form a free protruding end portion. This end portion and thus the whole bearing journal 13' and hereby the respective swivel wheel 11' can be direction controlled or steered, i.e. it can be given a definite angle in relation to the vehicle and its main chassis 7, at a special command and/or for some movement states of the wheeled chassis. Therefor a steering motor 19 is arranged receiving energy from the batteries 9 which is controlled and activated and deactivated as commanded by the control circuits 5. An endless element such as a chain or a cogged belt 21 passes around a wheel 22 driven by the steering motor 19 and also around cogs or teeth arranged on the protruding portion of the bearing journal 13', e.g. on a toothed wheel or gear wheel rigidly attached to this end portion. The motor-driven chain wheel or toothed wheel 22 is attached to an output shaft 35 (see also Fig. 5) of a reduction gear unit 23, which is connected, at its input shaft, to the output shaft of the steering motor 19, for instance being a part thereof such as is illustrated by the integrated motor/reduction gear unit of Fig. 5. The reduction gear unit 23 has in a practical embodiment a reduction ratio of 30:1 and is a conventional, not self-braking or not irreversible gear unit of the worm gear type having a worm 29 attached to the output shaft 31 of the steering drive motor 19 and having a worm wheel 33 cooperating with the worm 29 and having an output shaft 35, on which the wheel 22 (Fig. 2) is mounted. Instead of a gear worm unit naturally a corresponding easily rotatable gear wheel unit can be used. A position sensor or angular sensor is further arranged at the swivel pin 13', e.g. at the protruding portion thereof, and is attached to the rear frame 15 by means of some support 27. The angular sensor 25 delivers signals through lines, not shown, in regard of the angular position of the swivel pin 13' and these signals are provided to the control circuit. As has been mentioned above the drive motors 3 for the rotationally driven motors 1 are controlled by control circuits 5. These control circuits 5 can decide that also the steering of the rear swivel wheel is activated or deactivated for suitable driving situations. An instability when running the vehicle happens for movement states which roughly can be determined guided by the commands as provided by the driver in regard of the direction steering of the vehicle, which commands can be translated by the control circuits to desired values for the rotational velocity and the rotational direction of the driven wheels. The control circuits can use these commands or directly the desired values as calculated therefrom to activate or deactivate the angular steering control of the swivel wheel. Therefor the control circuits can contain algorithms which will partly be determined by experience and experiments for a particular vehicle. The angular steering control of the swivel wheels can in a special simple case be performed only when the vehicle has obtained such commands that the two driven wheels are to rotate in the same direction. Alternatively there may be provided on the vehicle a push button, an operating lever or some other operating means, by means of which the angular control of the swivel wheel can be deactivated. When the rear swivel wheel 11' is steered, the rotation or pivot angle of the swivel pin 13 can be adjusted so that the wheel 11' will obtain essentially that direction which the swivel wheel 11' will take if the vehicle was driven on a smooth horizontal ground and if this swivel wheel 11' could adjust itself freely. When the steering control of the rear swivel wheel 11' is not activated, this wheel can freely adjust itself in the same way as any swivel wheel and in particular in the same way as the other swivel wheel 11 arranged in parallel. It is rendered possible by the not self-braking reduction gear unit 23 and by the fact that the rotor 37 of the direction control motor 19 has a small inertia and is easily running or easily rotatable when the motor 19 is not activated. In Fig. 4 an electric block diagram for the wheeled chassis is illustrated. A lever or joystick 501 delivers a first analogue signal "Desired Velocity" in regard of the velocity as desired by the driver to a first electronic conversion and limiting circuit 503 which performs a conversion of the incoming signal to a digital shape and further limits the signals to only represent velocities for which the wheel-chair can be displaced safely. From the unit 503 a signal designated "VELOCITY OUT" is delivered, which thus in a digital shape represents the velocity as desired by the driver. The signal is provided to among other units a second electronic conversion and limiting circuit 505, which receives from the lever 501 a second analogue signal, in regard of the direction as desired by the driver and designated "Desired Direction". The second unit 505 performs in the same way a conversion to a digital shape of the incoming analogue signal and further various limitations of the output signal which in the corresponding way represents the direction as chosen by the driver of the wheel-chair and which is designated "DIRECTION". The limiting or restriction of the direction as chosen is made in dependence on various limiting factors, among other things the received velocity signal "VELOCITY OUT". The two digital signals from the first and second circuits 503 and 505 "VELOCITY OUT" and "DIRECTION" respectively are delivered to a calculating unit 507 which calculates primary desired values for the velocity of the driving wheels 1. Principally the velocity of the outer wheel when running in a turn or a bend is given by the signal "VELOCITY OUT" and the velocity of the inner wheel by the difference: "VELOCITY OUT" - "DIRECTION". The primary signals of the desired values produced by the calculation unit 507 are delivered to processing steps for the left drive motor and the drive motor for the right wheel. Only the processing steps for the left wheel are illustrated in detail in the Figure. The primary desired value signal for the left drive motor is thus first delivered to circuits 509 which perform a further filtration and a correction of the signal for providing a final desired value signal to a motor control circuit 511. It then provides an output signal directly to a driver step 513 for the delivery of pulsed driving energy to the motor 505 for the left drive wheel. The current and voltage of the driving motor 515 are fed back to circuits 517 for generation of an actual value in regard of the rotational velocity of the driving motor. The circuits 517 contain converters from analogue to digital shapes and circuits for calculating, from the values of the current and the voltage, the rotation velocity of the motor. The values generated by the circuits 517 are provided to the motor control circuits 511 for generation of the output signal thereof so that the desired value signal and the signal indicating the actual value are regulated to a difference which has a so small absolute value as possible. The primary signals "VELOCITY OUT" and "DIRECTION" are also delivered to a unit 519 for the calculation of a desired steering value for the swivel wheel 11' which is steered or direction controlled. This calculated desired value is in turn provided to regulation circuits 521, which deliver their output signal to a driver step 523, from which a suitable activation energy is provided to the steering control motor 19. The output signal of the direction sensor 25 is delivered to an A/D converter 525, the output signal of which is fed to the regulating circuit 521. The regulating circuit 521 hereby receives both a desired value and an actual value of the angular position of the steered wheel and provides a regulated output signal, so that the absolute difference of these two input signals will be as small as possible.

Claims: CLAIMS 1. A wheeled vehicle having rotationally driven wheels and having one or several freely rotating swivel wheels comprising a swivel shaft, about which the swivel wheel can be pivoted or rotated when the vehicle moves, to take different angles in relation to the movement direction of the vehicle, a selectively connectable or engageable, forced steering control or direction control being arranged to act on at least one freely rotating swivel wheel, this control being arranged to give, in the movement of the vehicle, this swivel wheel an angle in relation to the vehicle, which is variable and is adapted to the movement state of the vehicle, the control comprising - an electric rotational motor having an output shaft, - transmission means for transferring a rotational movement of the output shaft to a rotational movement of the swivel shaft of the swivel wheel, characterized in that the electric motor and the transmission means are constructed in such a way that they are not self- braking or not irreversible or in particular in such a way that when the electric motor is not provided with electric current, a rotational or pivoting movement of the swivel wheel about the swivel shaft owing to a movement of the vehicle and the cooperation of the wheel with a ground are then not obstructed b the transmission means or by the electric motor. 2. A wheeled vehicle according to claim 1, characterized in that the transmission means comprises a reversible or not irreversible worm gear unit for reduction of the rotational movement of the output shaft. 3. A wheeled vehicle having rotationally driven wheels and having one or several freely rotating swivel wheels comprising a swivel shaft, about which the swivel wheel can be rotated or pivoted when the vehicle moves in order to take various angles in relation to the movement direction of the vehicle, a selectively connectable or engageable, forced direction or steering control being arranged acting on at least one freely rotating swivel wheel the control being provided to give, when the vehicle moves or runs, this swivel wheel an angle in relation to the vehicle, where this angle is variable and is adapted to the movement state of the vehicle, characterized in that the control comprises - an electric rotational motor having an output shaft and having a rotor, which is rigidly attached to the output shaft and which is easily rotatable also when electric current is not fed to the motor, - a reversible reduction gear unit, in particular a worm gear unit, connected to the output shaft of the electric motor for reduction of the rotational movement of the output shaft and comprising an output shaft, and - stiff transmission means for transferring a rotational movement of the output shaft of the reduction gear unit to a rotational movement of the swivel shaft of the swivel wheel and therewith the rotational movement of the swivel wheel and for transferring a rotational movement of the swivel shaft to the output shaft of the reduction gear unit. 4. A wheeled vehicle according to claim 3, characterized in that the stiff transmission means comprises an endless element and wheels or pulleys cooperating therewith.

Inventors: ENGMAN BO, FARM GUNNAR, ENGMAN, BO, FARM, GUNNAR
Applicants: ENGMAN BO, FARM GUNNAR, PERMOBIL AB, ENGMAN, BO, FARM, GUNNAR
Application year: 1994
Main classification: A61G5
IPC codes: A61G5, B60L15